A lithography technology that an ArF excimer laser is used as a light source is used in fine pattern formation in a semiconductor manufacturing process. Since practical application of EUV (Extreme Ultraviolet Lithography) which is a next generation exposure light source of a shorter wavelength is delayed while pattern refining is being progressed, lithography near a resolution limit that a fine pattern of the size which is a fraction of a wavelength is formed using an ArF lithography technology comes to be performed. An OPC (Optical Proximity Correction) technology of correcting a mask pattern shape and an exposure light source shape by taking proximity effect of light into account is essential for the lithography near the resolution limit. For optimization of the OPC correction, it is necessary to modify a mask and a light source shape by measuring a sample (hereinafter, referred to as a fine resist sample or a resist sample) having a fine resist pattern created by actually transferring a mask pattern and evaluating a gap between it and design.
A scanning electron microscope (SEM) is used for measurement of the fine resist sample. However, when an ArF resist sample is to be measured by using the SEM, contraction (shrink) of the pattern of the resist sample caused by irradiation with an electron beam is generated and the dimension and the shape are changed. Therefore, in order to accurately measure the dimension and the shape of the pattern of the fine resist sample, it is necessary to accurately estimate shrinkage of the resist pattern and to correct it. In addition, since the resist sample is generally an insulator, there are cases where charging occurs on the sample surface caused by irradiation with the electron beam. In a case where charging occurs, the orbit of an incident electron beam is changed and some of signal electrons generated from the sample are brought back by positive charging of the sample surface, and an SEM image locally gets dark. As a result, there are cases where an error occurs in the dimension and the shape determined from the obtained SEM image. Accordingly, in order to accurately measure the pattern dimension and shape of the fine resist sample, it is necessary to also correct the error caused by charging.
As a method of estimating the shrinkage of the resist, the following method is indicated in Patent Literature 1. This is a method of estimating the shrinkage by measuring the resist sample a plurality of times by the SEM and obtaining a relation (a shrink curve) between a number of measurements and a change amount of the pattern dimension of the resist sample.
In addition, as a method of correcting the shrinkage in SEM observation of a two-dimensional pattern, the following method is indicated in Patent Literature 2. This is a method of adding a fixed value to a displacement amount of an edge position in the second and succeeding measurements such that an average value of the displacement amounts of edge points matches the first measurement in order to correct the influence of shrink in a case where measurement has been performed a plurality of times in measurement of a displacement in edge position between an acquired pattern shape and a reference shape.
In addition, as other methods, a method of correcting a contour by determining changes in dimension and shape due to shrink and an error due to charging by collating a database in accordance with a pattern shape of a sample, and a method of correcting a change in sample pattern position by calculating a stress between pattern parts of the sample are indicated in Patent Literature 3.